The objective of this grant application is to become one of the core clinical centers in the proposed Blood and Marrow Transplant Clinical Research Network. There are a number of features of the Fred Hutchinson Cancer Research Center (FECRC) Marrow Transplant Program that make it an attractive candidate for inclusion in the Network. First, we have maintained a large, stable transplant program for several decades transplanting between 450 and 550 patients per year with excellent clinical outcomes. Thus, we have access to a relatively large number of patients. Second, our group includes a large number of investigators focused on the general topic of transplantation. This group is supported by seven P0ls and 23 R0ls, and last year published 142 papers on the topic. Thus, our inclusion will help assure a source of possible studies for future testing in the Transplant Network. Third, our program is deeply committed to cooperative clinical research. For example, last year 231 of 451 patients transplanted in Seattle (51%) were entered onto multi-institutional trials. Finally, the FHCRC provides an outstanding environment in which to conduct the sorts of studies described, with state-of-the-art clinical and laboratory facilities. The proposed Blood and Marrow Transplant Clinical Research Network has the potential to facilitate studies leading to substantial improvements in the outcome of transplantation. Inclusion of the Fred Hutchinson Cancer Research Center in this network should help it achieve this goal.